There are used devices for movement and orientation of objects in space, for example to carry out high precision machining and/or high speed machining. The object whose movement and orientation is ensured, can be constituted by a tool or else by a piece on which machining is performed.
In particular, there should be in certain industries machine tools such as milling tools to carry out high speed machining whose movement can be carried out, for example on five axes of which three axes of movement in translation and two are axes of movement in rotation.
More generally, in the case of machines for machining of complex shape or systems of manipulation of objects with high precision, it may be necessary to use devices for movement comprising at least two axes of movement in translation and two axes of movement in rotation.
Until now, such devices and in particular milling tools with digital control used in industry used a construction of serial type, which is to say a construction in which the axes of movement and the corresponding motor means are mounted in series. There exist several families of devices or machines that can be classified according to their number of degrees of freedom. The most common machines are machines with three, four or five axes, which is to say with three, four or five degrees of freedom. Such machines using constructions of the serial type are less adapted to the needs of high speed machining, because of their high inertia, an upstream axle of the machine having to support a downstream axle and its motor means.
For this type of use, it is thus desirable to use constructions of the parallel type, which is to say comprising motor means carried by a fixed frame of the machine, with a non-driven transmission of the movements of the different portions of the device.
Until now, machine tools of the parallel type with at least five degrees of freedom of movement of a tool or of a workpiece use principally an architecture of the “Gough-Stewart” type, these machines being called hexapodes machines. Such hexapodes machines have a direct geometric design which has up to forty solutions and whose frontiers as well as the position of the singular configurations are difficult to characterize. Small variations of parameters of design can lead to important modifications as to the stability of the direct geometric model and performances of such machines. Moreover, the faculties of orientation of the hexapodes machines are very limited. In the case of a machine tool such as a milling tool with five axes, a hexapode machine requires the management of the redundancy because of the fact that it has six degrees of freedom.
There is also known a hybrid device with five degrees of freedom comprising a carrier of the parallel type and a spherical joint of the serial type. These actuators of the carrier are not fixed and the movement produced by these actuators is not a simple movement of translation. There exist twenty-four solutions to the direct geometric model of this device and there exist no unitary domain in the working space. To maintain the spindle with a constant orientation, it is necessary to change the orientation of the spherical joint. Moreover, the carrier must support the weight of the joint and of its motors.
In the field of high speed machining, for example for the production of milling tools, it is thus desirable to use devices for movement and orientation of tools, of the parallel type, which have a simple geometric and kinematic design as well as a working space of regular and perfectly defined frontiers. It is necessary also that the kinetostatic properties of the device be near those of a conventional machine tool, and to do this, that the device have an isotropic configuration in its working space, with control of the position and of orientation. Moreover, the factors of amplification of the speed of the device must remain limited to all the accessible working space.
There is known a device for movement in space of an object along three axes in translation, which comprises three legs in the form of parallelograms mounted in an articulated manner at a first end, each on a movable element moved by means in translation, carried by a fixed frame, along a slideway carried by the fixed frame and at a second end, on a support of the object to be moved. Such a device does not permit carrying out orientation of the object according to at least two axes, by control from the fixed frame.
There is also known from U.S. Pat. No. 5,966,991 an orientation device of the spherical joint type which comprises two actuators for driving in rotation along two axes on which are mounted first ends of two arms whose second ends are mounted in articulation, for the one, on the support of the object, and, for the other, on an intermediate arm itself mounted articulatedly on the object support.
All the axes of articulation and for driving in rotation of the device are concurrent at a center of spherical rotation of the device. For its actuation, such an orientation device requires the use of actuators in rotation along the axes of which are fixed the arms of the spherical orientation device. These devices for movement in space and orientation, known in the art, are not made in a way enabling them to be associated to constitute a system of movement and orientation of the parallel type.
WO 02/85580 discloses a device for moving a tool of the parallel type. These movements in translation of the tool are transmitted by articulated legs and movements of rotation are transmitted to the tool by axles mounted in the longitudinal direction of the legs.
However, the device does not comprise a mechanism for orientation at the center of spherical rotation.